Internal combustion engine



De@ 22, l942- E. E. wlLsoN ErAL 2,305,946

INTERNAL COMBUSTION ENGINE Filed Sept. 7, 1937 3 Sheets-Sheet l Dec. 22, 1942. E. E. WILSON ETAL INTERNAL COMBUSTION ENGINE Filed sept. 7, 1937 s sheets-saw@ 2 DeC- 22, 1942- E. E. wxLsoN ErAL INTERNAL COMBUSTION ENGINE Filed sept. 7, 1937 3 Sheets-Sheet J5 atented Dec.` 22, 19742v 2,305,946 i INTERNAL COMBUSTION ENGINE Ernest E. Wilson, near Milford,

ma John o.

. Almen, Royal Oak, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation ot Delaware Application September 7, 1937, Serial No. 162,690

(Cl. 12S-52) 4 Claims.

We have discovered that operating characteristics of an internal combustion engine, such as its noise producing characteristics,its rate of i fuel consumption, its tendency. to detonate, itsv power output and the temperature of its exhaust gases, are to a very considerable extent affected,v

not only by the resistance of its intake and exhaust systems to the flow of gases therethrough, but also by the acoustical characteristics of its intake and exhaust systems. By the term acoustical characteristics is meant the properties of the intake and exhaust systems with rey gard to their effect on the phase relations in which the pressure Waves which occur therein while the engine is operating merge and to the creation of resonance of thesepressure Waves.

We have also discovered that the acousticalcharacteristics of the intake and exhaust systemsl of an internal combustion'engine maybe altered and that when they are altered the operating characteristics of the engine are altered. And, upon the basis of these discoveries, we have devised a procedure by which defects in the acoustical characteristics of the intake and exhaust systems of van internal combustion engine may be detected and the alterations necessary to eliminate them and thereby favorably influence the operating characteristics of the engine determined. In this procedure and inthe improvements in internal combustion'engines which have resulted from its application resides the invention to which this application relates.

Although some features of this invention are applicable to single-cylinder internal combustion engines and to multi-cylinder internal combustion engines equipped with' independent intake and/or exhaust systems for each cylinder, the invention has to do principally with multicylinder internal combustion engines equipped with intake and exhaust manifolds. To understand and appreciate our invention fully, some comprehension of the phenomena which occur in the intake and exhaust systems of multi-cyldenite natural frequencies.

inder internal combustion engines equipped withv intake and exhaust manifolds is necessary.

It is, of course, a matter of common knowledge that during the operation of an engine of the typenear consideration, air or a mixture of fuel and air enters its cylinders through its intake manifold and burned gases are Vdischarged from 'its cylinders into the atmosphere through its exhaust manifold.l It is commonly known that because the air or the mixture of fuel and air enters-and the burned gases are discharged from each cylinder, not continuously, but intermi tently, the flow of the air or the mixture of fuel and air and the burned gases is, not smooth and steady, but pulsating. The effect of the inter-A mittent introduction and discharge of air or a described differently by saying that it produces in the intake -and exhaust systems pressure waves which travel at approximately 4the speed of sound. Each of the cylinders produces its own series of pressure waves and the pressure waves produced by one cylinder naturally affect the ingress of air or the mixture of fuel and air into and the exit of burned gases from the other cylinders.

The intake and exhaust systems of an internal combustion engine may be considered pipes of xed length which are closed at the (engine) ends near which the pressure 4Waves originate and are open at their opposite ends unless there are incorporated therein baille mufliers in which event they are to be considered pipes closed at both ends. The intake and exhaust systems of internal combustion engines, consequently, have In View of this and the facts that the intake and exhaust periods of the several cylndersoccur at different instants and that the ports of the several cylinders are commonly at different distances from -the atmosphere, the pressure Waves produced by i characteristics of the engine either favorably or unfavorably.

Generally speaking, resonance or a union of pressure waves in phase is a desirable condition in the intake system because it generally tends to 'increase the pressure therein when the intake ports are open and, consequently, the volume of combustible mixture or air which enters the cylinders of the engine and an undesirable condition in the exhaust system because it generally tends to increase the pressure therein when the exhaust ports' are open and, consequently, to decrease the volume of combustible mixture or air whichenters the cylinders by hindering the discharge of burned gases therefrom. Conversely, generally speaking, aunion of pressure waves out of phase is an undesirable condition in the intake system and a desirable condition in the exhaust system.

The determination of the acoustical characterisi-.ics of the intake and exhaust systems of an internal combustion engine, the defects, if any, therein and the alterations necessary to eliminate the defects is preferably made by analysis o! the variations in the pressures within a cylinder of mixture of fuel and air and burned gases may be `the engine and within its intake and exhaust manifolds near the cylinder during the intake and exhaust periods of the cylinder. But an alternative method of determination of the mentioned characteristics, which is applicable to proposed as Well as to existing systems and, consequently, eliminetes much experimental work and testing, is available, elle., e study of the intake and exhaust timing ci the cylinders of the engine in conjunction with the nains' order of the cylinders and the structurel characteristics ci the systems.

How the intelre ond l sust systems of an internal combustion engine they ice slt-.ered to change their acoustical characteristics end what effects these changes here on the acoustical characteristics of the systems will be fully set forth in the following sneciilcetion.

For a better und-e1 tending oi the nature and objects oi' this invention, r erence is inode to the following sneciicet' the accompanying drawings wherein the invention end its application to two Iinter el combustion engines is described end illustr in the eccomper leanings: Y

Figure 1 is e, side e tion of en interne-l cornbuetion engine eeulonecl with complete intake and,.exhausd systems..

Figure P is c 'ton 'view ci the engine shown in Figure which the Variations in er end Within. the,` intake oi the engine shown in exhaust nien. olds meines end 2 nliicelly represented. l not?, in side elevation, e en shot/"e in t, .res l end 2 equipped modified systems. "new top pien, in ton Wei?, end in eleve-e cwest end in section, rw 'Figures and 2 :e systems. on ci another tornei :intetlre elevation, the engine esuinned e rhodent positions oi e oreille shaft during exhaust periods ci 4the engine while tee engine is equipped with its complete intake sind exheust systems. :in the cases of variable engines, the prescribed data should insteken While the engine is operthe cylinder .tout different ifi ating at several din :ent speeds lout, in the cases of constant speed engines, the dette need he taken.

only while the engine is operating at the speed at which it is designed to operate. The prescribed data may be obtained by means of any suitable pressure recording gauge.

The next step, in accordance with the preferred procedure, consists in analyzing the data obtained during the nrst step to determine the acoustical' characteristics of the intake and exhaust systems of the engine, the defects, if any, therein, what features 0f the systems produce these defects, and how the systems may be altered to eliminate the defects.

The third and nal step, in accordance with the preferred procedure, is to alter the intake system end/o1' the exhaust system of the engine in the manner indicated by the analysis mede during the second step.

To supplement the foregoing outline ci our invention and to render 'the nature and epplicetion of the invention more readily comprehensible, We shell show how it has been applied to the two internal combustion engines shown in the drawings.

The first oi? the engines which are to loe considered is shown in Figures l and 2. This engine, which is the propelling engine of e. 'avell known maire of automotive vehicle, is e. straight-eight of the ounstroke cycle type whose cylinders, numbered consecutively from front 'to of engine, re in the order l, 5, 5, i3, 7l, Each of the cylinders of the engine is equipped with e. poppet nteke valve which opens 22D before top deed center end closes i' citer hottorn center and with a poppet exhaust in ve which opens 57 before bottoni deed center und closes 29 after top dead center.

The intake system of the engine shown in Figures l and 2 consists of s, combiner and silencer 'til ci the resonetonehsorcci duel updrait carburetor which consists oi two rtuiners f of "which each is connected et its mid-'point te one the combustible mixture discherge orifices of the cerk buretor 3i. The runner '.ll is connectedv et one end to the intake ports oi the iirst Wnd second. and et the other encl 'to the intuire ports ei the sev ith and eighth cylinders: of the engine. The runner is connected at one end to the intake of the third and fourth end at the other enc. the intake ports ci the fifth and sixth cylinders or? the engine.

The exhaust system of the engine includes rneniiold which consists of e single runner 31 with ve bronches 35, 3l', 3l? end which are connected, respectively, to the st, second .end third, fourth and fifth, sixth c, seventh, end eighth cylinders of the engine. To the end oi the runner 3ft opposite the loretnoh there is connected an exhaust pipe fit to whose outer end there is connected a through-type resonator muffler 4l. To the outer end 0i the houiller ti, there is connected e tail pipe d2.

The prescribed detta with respect to the pressures Within e. cylinder and within the intuir end exhaust manifolds of the engine shown in Figures l and 2 near the cylinder was teken while the engine was operating at several difierent speeds. Curves Which represent the veriations in pressure at the designated points in units of pounds per square inch above and below etmospheric pressure plotted against crank angle in terms of piston position while the engine was operating at speeds ofv 400, 300, 1600 and 2800 R, P. M. are reproduced in Figure 3. In this ligure, the solid line curves represent the varia.-

tions in the pressure within the cylinder, the dotted line curves the variations in the pressure within the intake manifold, and the dash line curves the variations in the pressure within the exhaust manifold.

An examination of the curves shown in Figure 3 discloses two noteworthy features. One

-is the regularity and large .amplitude of the pressure variations in the exhaust manifold at the speed oiy 800 R. P. M. The other is the high value of the pressure within thel cylinder at the beginning of the intake period and at top dead center on the exhaust stroke at this speed of the engine.

The iirst feature indicates that resonance of pressure wavesoccursy in the exhaust system at the' speedof 800 R. P. M. and, consequently, that theengine does not have optimum operating characteristics at this speed. The existence of this condition, which was manifested in the engine under consideration by an increase in its noise producing characteristics and a loss of power at the speed of 800 R. P. M., might have been predicted from a consideration oi its ilring frequency and the effective length of its .exhaust system.

The high value of the pressure within the cylinder at the beginning of the intake period and at top deadcenter on the exhaust stroke indicates that the cylinder is not completely rid of burned gases and, therefore, cannot be fully charged with combustible mixture and does not develop the maximum power oi which it is capable at the speed of 800 R. P. M.

The speed at which resonance of pressure waves occurs in the exhaust system of an engine depends upon the tiring frequency of the engine and the eiective length of its exhaust system and may, consequently, be changed by altering the eiective length of the exhaust system. Therefore, if resonance of pressure waves is particulariy objection-shire at the particular speed aty which it occurs, is possible to alter the exlia-ust system sopas to eliminate the condition at this speed.

The eiective length of the exhaust systernoi paternal combustion engine is approximately edu to the Volume its exhaust manifold divided the oros sectional. area oi its exhaust pipe, ce from the junction of the me "ioid and ust pipe to the outer end pipe engine is equipped with cre the lengt he piping included therein lout it should he :ed ont lthat a change in the length or the piping in an exhaust system in which a haine muler is included will alter the eective length of the exhaust system only if it is made on the engine side oi the first 'beide in the minder.

While the volume of the exhaust manifold of an internal combustion engine may, of course, be

. changed "by altering ius transverse dimensions or lengtim ci its oreinches, there are expediente 'oy which the volume ofthe exhaust manifold may increased and the effectivel length of the exhaust system thereby increased without alter'- iiig either of these dimensions. Some oi these expediente are illustrated in Figures 4, 5 and 6 of.

the drawings.

In Figure d there is shown the engine shown in Figures 1 and 2 equipped with a Y-type exhaust manifold. This manifold consistsof two runners and 44 which'are. joined one to the other and connected to thesame exhaust pipe 4l at their inner ends. The runner 43 is con- Y nected to the first, second, third and fourth and the runner 44 to the fifth,l sixth, seventh and eighth cylinders of the engine. The manifold shown in Figure 4 diilers from conventional Y- type manifolds in that the runners 43 and 44 are extended beyond the front and rear exhaust ports of the engine, as indicatedat 45 and 46, in order to increase the effective length of the exhaust system. The installation of a manifold of the type shown in Figure 4, of course, renders the exhaust system of the engine on which it is installed equivalent to a pipe closed at one end with the source of the pressure impulses (the engine) between its ends.

The extensions 45 and 4B of the exhaust manifold shown in Figure 4 may be replaced by chambers of larger cross-sectional area than the runners 43 and 44. The manifold shown in Figure 4 modiiied in the manner suggested in the next preceding sentence is shown 'in Figure 5 in which the reference characters 48 and 49 represent the chambers referred to. A merit of this installation is its economy oi space.

The eiiective length of the exhaust system of the engine shown in Figures 1 and 2 may he increased by connecting the rear end of the runner 34 to the exhaust pipe 40 so as to produce what A may be called a loop manifold. The engine shown in Figures l and 2 equipped with such a loop manifold is shown in Figure 6. This manifold consists oi a runner 4l which is connected to the exhaust ports of all of the cylinders of the engine and outlet ducts 50 and 5l, oi which the former is longer than the latter. The inner ends o the outlet ducts 5E and 5i are connected9 respectively, to the front and rear ends oi the runner 4l and the outer ends thereof are joined one to the other and connected to the same exhaust pipe 40.

By any of the expedients which have been suggested, the edective length ofthe exhaust system or an internal combustion engine may be altered so as to eliminate. resonance of pressure waves at any given engine speed or at all speeds at which the engine is designed to operate or as to create resonance of pressure Waves at any desired engine speed.. Elimination oi resonance of pressure Waves at all engine speeds may also, in efiect loe'eccomplished by so tuning the tuning pipes which the extensions d5 and 46 oi the runners oi manifold shown in .Figure 4 constitute or the bottle-type resonators which 'the chambers iii and Si and the extensions of the runners of the manifold shown in Figure 5 to which they are connected constitute that their natural frequencies are equal to the natural fre" quency of the exhaust system because, when the tumngpipes or the resonators are so tuned, they will attenuate by resonance the pressure waves which are subject to reinforcement by resonance.

fit is quite clear that the high value of the pressure Within the cylinder of the engine shown in Figures i. and '2 at the beginning of the intake period and at top dead center on the exhaust stroke is not attributable to any action of the cylinder under consideration. Our experiments have shown that this high pressure conditionl is attributable to the arrival at the exhaust port' of the cylinder under consideration near the end of its exhaust period of the peak of a pressure impulse from another cylinder which impedes the discharge of burned gases from the cylinder under consideration. Consideration of the timing and the firing frequency of the engine renders it quite clear that the troublesome pressure impulse is produced by the cylinder which fires second (180) after that under consideration.

The foregoing explanation of the cause of the undesirable pressure condition within the cylinder Aunder consideration renders it clear that its existence might have been predicted from a consideration of the factors which determine the interval in the cycle of operation of one cylinder at which pressure impulses from the other cylinders reach its exhaust ports, viz., the firing'order, the firing frequency and the timing of the engine and the distance which pressure impulses from one cylinder must travel to reach the exhaust ports ofthe others. Generally, as we have intimated above, except in connection with large engines, the iirstand last mentioned factors need not be considered in. determining whether and, if so, at what engine speed the undesirable pressure condition under consideration will occur.

From what has been said, it quite apparent that, if the pealr. oi the pressure impulse from the cylinder which fires 180 after that under consideration did not arrive at the exhaust port of the latter near the end oi' its exhaust period, the pressure within the latter at the beginning ci? its intake period and at top dead center on its exhaust stroliev would be reduced and, consequently, that the operation oi the engine at the speed of 800 R. P. lill. would be improved. Consideration of the fact that the pressure impulse travels at a definite rate of speed shows that, by changing the distance which the pressure impulse must travel to reach the exhaust port of the cylinder under consideration, it is possible to prevent its peak arriving at the exhaust port of the cylinder under consideration near the end of its exhaust period, vf course, this can be done by simply changing the length oi the runner of the exhaust manifold between the cylinder under considera-- tion and the cylinder which rires 180 after it but we consider it preferable to do it by subdividing the manifold so that no two cylinders which re 180 apart exhaust into the same runner.

In Figures 'l and 8, there are shown exhaust manifolds for the engine shown in Figures l and 2 subdivided as suggested above.

The exhaust manifold shown in Figure 'l consists of two runners and 53 on which there are formed outlet nozzles Sil and dii. The runner di is connected to the exhaust ports of the first, fourth, ith and eighth and the runner 33 to the exhaust ports of the second, third, sixth and seventh cylinders of the engine.

The exhaust manifold shownin Figure 8 consists of-two runners and 5l on which there are formed outlet nozzles liti and liil. The runner 5E is connected to the exhaust ports of the first, third, sixth and eighth and the runner El lto the exhaust `ports oi the second, fourth, fth and seventh cylinders of the engine.

The nozzles ,it and 55 of the exhaust manifold shown in Figure 7 and the nozzles titi and 59 of the exhaust manifold shown in Figure 8 may be connected to separate exhaust pipes and therethrough to separate mufilers and tail pipes. Or, as the drawings indicate, the nozzles M and 55 may be connected to the same exhaust pipe 6D, muffler 4i and tail pipe 42 by a Y El and the nozzles 58 and 59 may be connected to the same exhaust pipe, muler and tail pipe by a Y 62. However, if the two nozzles of a manifold, such as those shown in Figures l and 8, are connected to the same exhaust pipe, mufer and tail pipe, as shown in the drawings, it is possible that the pressure impulses from a 'cylinder which exhausts into one runner may, at the junction of the branches of the Y, unite in phase with and reinforce the pressure impulses from a cylinder which exhausts into the other runner and/or may, by traveling through the branches of the Y, reach the exhaust port of a cylinder which exhausts into the other runner at such an interval in the cycle of its operation that it impedes the discharge of burned gases therefrom. But since ,the pressure impulses travel at a definite rate oi speed, it is possible to eliminate both of these contingencies, throughout a considerable range of speed of operation of the engine, if not throughout the entire range of speed thereof, by making one branch of 'the i of greater length than the other, as shown in the drawings, and properly dimensioning the total length. of the branches. And, furthermore, by an extension of the former expedient, viz., by making the diiierence between the lengths of branches of ...e Y such that the pressure impulses the cylinders which exhaust into one runner of manifold reach the junction of the branch the Y 180 out of phase with the pressu pulses from the cylinders which exhaust i the other runner at any selected s of the engine, it is possible to cause the pressure impulses to attenuate each other very considera only at the selected speed, but also throughout a considerable range of speeds which extends above and below the selected speed.

ders of the engine shown in .Figure 6 through both of the outlet ducts ll and junction thereof, there is the saine possi" that pressure waves will be reinforced a' r pressure waves from one cylinder will impede discharge of burned gases from anotherI cylinder' in the manifold shown. in Figure 6 as in the ex.m haust systems shown in Figures '7 and 8. l-Iow ever, both of these contingencies may be climi'- nated in the manifold shown in Figure S use of the expedients discussed in connection with. the exhaust systems shown in Figures 7 and 8, viz., by making the outlet ducts E@ and iii of the proper absolute and relative lengths. it will, therefore, be understood that the total length of the outlet ducts Fail and 5l shown in Figure G is such that the latter contingency is eliminated and that the difference in the lengths of ducts which has been mentioned is such that the former contingency is eliminated.

instead of an exhaust manifold which consists of two runners, such as those shown in Figures l and 8, theengine shown in. Figures 1 and 2 may be equipped with an exhaust manifold which consists of four runners oi which each is connected to the exhaust ports of two cylinders or with a separate exhaust flue for each cylinder. Each of these runners or exhaust nues may be con nected to a separate exhaust pipe, muffler and taii pipe. Or, alternatively, the several runners or exhaust iiues may be connected to the same exhaust pipe, mullier and tail pipe by ducts of such absolute and relative lengths that the contingencies l mentioned during the discussion of the manifolds shown in Figures 7 and 8 will be eliminated.

A change in the volume of the exhaust manifold whichhas 'been mentioned as an expedient by which the effective length of the exhaust system of an internal combustion engine may be a1- tered affects also the amplitude of the pressure waves in the system but not the interval in the cycle -of operation of one cylinder at which the -peaks and valleys of pressure waves from the resides in increasing the lengths of the branches other cylinders reach its exhaust port if the transverse dimensions only of the manifold are laltered. It is, therefore, possible to reduce the high value of the pressure within the cylinder of theengine under consideration at the beginning of its intake period and at top dead center on its exhaust stroke at the speed of 800 R. P. M. withl out changing the interval in its cycle of operation at which the peak of the pressure wave from the cylinder. which iires second after it arrives at its exhaust portby increasing the volume of its exhaust manifold by increasing its transverse dimensions only.

An examination of the curvessnhown in Figure 3 will also reveal the defects in the intake system of the engine shown in `Figures 1 and 2 and indicate how it should be altered to eliminate them.

In deducing from the curves the defects in the intake system and the remedies therefor, the principles employed in connection with the exhaust system are applicable. However, certain essential differences between the intake and exhaust systems of an internal combustion engine must be taken into account in applying these principles. Particularly, vit must be remembered that high pressure in the intake manifold at the intake port of the cylinder of an engine, particularly near the end of its intake period, is an aid to the introduction of a full change of combustible mixture into the cylinder and is, consequently, a desirable condition. Therefore, a union of pressure waves in phase, the arrival of a peak of a pressure wave at the port of a cylinder near the end of its intake period and resonance of pressure waves are generally to Ibe sought rather than avoided in the intake system of an internal combustion engine. visible to employ the expedient or decreasing the ltransverse dimensions of the intake manifold,

particularly the portion of it near the intake ports, to produce the desirable condition referred to.

How the intake system of an internal combustion engine may be altered to effect the union of pressure Waves in phase and/or to insure the arrival of-a pressure impulse at the port of a But generally it is not 'adcylinder near the end of its intake period muy, Y

we think, be deduced from the foregoing discussion of these phenomena.

To obtain resonance of pressure waves in the intake system o an internal combustion engine,

it is generally necessary to increase the eective length of the system. And it mayhere be .pointed out that if the eective length of the intake system is increased sumciently resonance of pressure waves will occur at two speeds of the engine-at the lower speed because the frequency of the pressure impulses produced by the engine equals that of the fundamental and at the higher speed because the frequency oi these pressure impulses equals that oi a harmonic of the system. Any of the expedients hereinbefore suggested in connection with the exhaust system of the engine shown in Figures l and 2 may be employed to alter the effective length of the intake system of an internal combustion engine but they should be applied with care in order to avoid unfavorably affecting distribution of combustible mixture to the several cylinders of the engine.

Some expedients by which the effective length of the intake system of the engine shown in Figures 1 and 2 may be lengthened are illustrated in Figures 10 and 11 of the drawings.

The expedient which is illustrated in Figure 9` 63 and 6I and 85 and It which connect the runners 6l and 68 of the manifold to the intake ports of the cylinders of the engine.

'l'he expedient, which is illustrated in Figure l0 which is more practicable than that illustrated in Figure 9 because it is less likely to introduce fuel distributiondiiculties into the intake system of the engine, resides in connecting a tube, which may be made adjustable in length, to the or each of the air intake orifices of the carburetor. To increase the effective length of a dual intake system, such as that with which the engine shown in Figures 1. and 2 is equipped by the expedient under consideration, a separate tube should be connected to each of the air intake orifices of the carburetor because the effective length of the sections of a dual intake system, considered as pipes, terminates at the junction, if any, of the sections. The engine shown in Figures 1 and 2, with its intake system modified as suggested above, is shown in Figure 10. In this figure, the reference characters'32 and 33 indicate the two sections of the intake manifold, the reference character 3l the carburetor and the reference characters 69 separate tubes of which each is connected to one of the air intake orifices of the carburetor. An air cleaner, a silencer or a combined air cleaner and. silencer may be connected to the outer end of each of the tubes 69. Or a single air cleaner, silencer or combined air cleaner and|silencer may be connested to the outer ends of the tubes 69 by a Y. But, in the latter event, neither the air cleaner, silencer or combined air cleaner and silencer nor' the Y can be considered in determining the effective length of the intake system.

The expedient which is illustrated in Figure ll resides in. connecting a bottle-type resonator lil,

which may be tuned or untuned, to each of the Each ci' the cylinders of the engine is equipped with a puppet intake valve which opens 43 before top dead center and closes d3 after bottoni dead center and with a, poppet exhaust valve which .opens and closes 62 after top dead center. y

The intake system of the engine shown in Figures l2 and i3 consists oi a combined air cleaner and silencer 8d of the resonator-absorber type, a. single downdraft carburetor 8i and a manifold which consists of a single runner tt connected by branches 83, 84 and t5 to the intake ports of the first and second, the third and fourth, and

' the fifth and sixth cylinders of the engine, re-

A To the outlet nozzle 86 of the lexhaust manifold spect-ively. The .exhaust system oi the engine includes a manifold 8l! whose branches 68, 89, 9d and 9i are connected, respectively, to the exhaust ports of the rst, the second and third, the fourth and fifth, and the sixth cylinders of the engine.

t1, there is' connected an .exhaust pipe 92 to whose outer' end there is connected a muiller 93 which, for the purpose at hand, is to be considered of the baille type. there is connected a tail pipe 94.

The prescribed data with respect to the pressures within a. cylinder and within the intake and To the outer end of the muffler 93,`

' Figure 14.

An examination of the curves shown in Figure 14 discloses two noteworthy features. One is the regularity and large amplitude of the pressure variations in the exhaust manifold at the engine speed of 1200 R. P. M. The other is the high value of the pressure in the cylinder at the loe-- ginning of the intake period and at top dead center on the exhaust stroke when the engine is cperating at speeds above 800 R. P. M.

The significance of the features to which attention has been called. will. loe understood :from what was said during the discussion oi the engine shown in Figures l. and 2. The resonance oi pressure Waves which occurs in the exhaust systern at the engine speed of 1200 R. P. ivi. can, ci course, he eliminated by changing the effective length of the exhaust system hy any of the expedients suggested during the discussion of the engine shown in Figures 1 and 2.

It is apparent from a consideration of the timing and iiring frequency of the engine shown in Figures 12 and 13 that the high value of the pressure in the cylinder at the beginning of the intalre period and at top dead center on theexhaust stroke is attributable to a pressure impulse from the cylinder which iires immediately 120) after the cylinder under consideration. This undesirable pressure condition may be eliminated by any of the expedients suggested during the discussion of the engine shown in Figures 1 and 2. An exhaust manifold for the engine shown in .FigliresA l2 and 13 which will accomplish the desired result is shown in Figure 15.

The exhaust manifold shown in .Figure l5 consists of two runners 95S and Elli on which there are provided outlet nozzles l and 08. The runner 95 is connected to the exhaust ports of the nrst, second and third and the runner se to the exhaust ports of the fourth, fifth and sixth cylinders of the engine. The outlet nozzles 2l and 98 may be connected to separate exhaust pipes, muiers and tail pipes or may be connected to the same exhaust pipe, niuilier and tail pipe by a Y in the manner disclosed during the discussion of the exhaust systems shown in Figures 6, 7 and 8.

Since when two cylinders whose intake periods overlap are connected to the same intake inanifold, one reduces the pressure available to introduce combustible mixture into the other, it is apparent from a consideration of the timing and ring frequency of the engine shown in Figures l2 and 13 that its operating characteristics cculd be improved by providing it with a multiple intake system, i. e., bv providing intake systems for the successively ring cylinders which are entirely separate or are separate except in that only a single carburetor is incorporated therein. And it will, of course, be understood that any of the expedients referred to during the discussion of the engine shown in Figures 1 and 2 may be employed to alter the effective length of and create resonance and/0r to insure union, in`

theme46 phase, of pressure waves in the intake system of the engine shown in Figures 12 and lli and/or to regulate the interval in the cycle oi operation of one cylinder at which pressure impulses from other cylinders reach into intake ports.

Although the experimental method of determining whether or not and, if so, at what speed of the engine resonance of pressure t'vaves occurs in the exhaust or the intake system of an internal combustion, engine and at what interval in the cycle of operation of a cylinder pressure irnpulses from another cylinder or cylinders arrive at its ports has been emphasised it is, ci course, within the scope of and a feature oi' this invention to determine these facts hy analysis of the factors upon which they depend without experimentation. ind although we have referred to the determination oi pressure conditions within and near a single cylinder only ci? an engine it will, of course, he understccd that if design ci the engine under con eration is such that the pressure conditions in near one cylinder are different from those 3. .l

near another cylinder or cylinders, it necessary to determine pressure conditions and near a number oi cylinders in order to dete'inine the acoustical characteristics of the engine, the defects 'therein how the defects eliminated. `also, although specifically does not constitute a eature of the invention with. which this application is concerned, it may be pointed out that the interval in the cycle of operation or a cylinder oi an engine at which pressure impulses from another cylinder or cylinders of the engine reach 'its ports :may be altered altering the timing of the engine or the rlovl characteristics of its ports.

We claim:

1. In a multi-cylinder four-stroke cycle internal combustion engine whose cylinders nre at intervals, an exhaust system which. includes a plurality" of ducts oi which each is connected to a plurality of cylinders oi which no pair rire at intervals of 2. in an eight cylinder four-stroke cycle internal combustion engine whose cylinders fire at 90 intervals in the order l, 6, 2, 5, 8, 3, 'i'. Li, an exhaust system which includes a duct which is connected to the nrst, fourth, fifth and eighth cylinders and a separate duct which is connected to the second, third, sixth and seventh cylinders.

3. "in an eight cylinder four-stroke cycle internal combustion engine whose cylinders nre at 90 intervals in the order 1, 6, 2, 5, a, 3, 7, 4, an exhaust system which includes a duct which is connected to the iirst, third, sixth and eighth cylinders and a separate duct which is connected to the second, fourth, fifth and seventh cylinders.

4. In a multi-cylinder internal combustion engine, a bifurcated duct of which oneibranch is connected to the exhaust ports oi certain and the other branch to the exhaust ports of the same cylinders of the engine, the branches being oi such total length that when the engine is operating at a selected speed pressure impulses from one of the cylinders travel through the branches of the duct and reach the exhaust port of another cylinder at such an interval in its cycle of operation that they do not materially obstruct the discharge of burned gases from it.

ERNEST E. WILSON. JOHN O. ALMEN. 

